Process for producing carbon black



Feb. 26, 1952 G. N. CADE PROCESS FOR PRODUCING CARBON BLACK Filed DGO. 5, 1949 Patented Feb. 26, 1952 OFFICE PROCESS FOR PRODUCING CARBON BLACK George N. Cade, Bartlesville, Okla., assignor to Phillips Petroleum Company, a.

Delaware corporation of Application December 5, 1949, Serial No. 131,129

Claims.

This invention relates to the production of carbon black. In one specific aspect it relates' to the production of carbon black in a furnace by pyrochemical action in which propertiesof the carbon black are improved by the presence of chlorinated hydrocarbons in the hydrocarbons being reacted to form the carbon black. In another specific aspect it relates to the production of larger amounts of carbon black than could normally be produced in such a furnace, but said carbon black containing tar which must be removed, and then utilizing said tar as removed by a chlorinated hydrocarbon along with a tar contaminated portion of said solvent in the reaction zone of said furnace to improve the quality of said carbon black. In another specific aspect hydrogen chloride is produced as a byproduct.

While the present process is applicable to any type of carbon black furnace with valuable results, it is particularly adapted to operate with carbon black furnaces having a circumferentially and/or helically moving blanket of air, air and fuel, flame, and/or hot combustion gases such as disclosed in the patent to Ayers Re. 22,886 June 3, 1947, Krejci Patents 2,375,795; 2,375,796 2,375,797 and 2,375,798 all of May 15, 1945 and all such similar carbon black furnace processes.

It has been found that in the making of carbon black in carbon black furnace processes that the total yield of carbon black, and the yield per unit of reactant hydrocarbon, lmay be increased when the rate of feed of said hydrocarbon is increased relative to the amount of free-oxygencontaining gas, such as air, supplied to the furnace, but that the carbon black so produced is commercially unacceptable to the rubber compounding industry and other carbon black consuming industries because of the high tar content. At -the same time some carbon blacksV so produced have a low Scorch time, that is, they tend to produce effects resembling premature vulcanization in rubber compounds in a relatively short compounding time, which short scorch time appears to be correlated with the high pH of such carbon black.

The present invention improves the qualities of such carbon black byremoving the tar with a chlorinated solvent, and by passing a portion of said solvent to the reaction zone of the carbon black furnace. The carbon black is formed in the presence of hydrogen chloride, which further improves the qualities of the carbon black, especially by increasing the Scorch time and lowering the pH, while at .the same time hydrogen chloride is formed as a valuable by-product.

One object of the invention is to produce increased quantities of commercially acceptable 'carbon black per furnace hour and/or per unit of hydrocarbon feed.

Another object is to produce carbon black having improved qualities such as increased Scorch time and/or lowered pH.

Another object is to produce hydrogen chloride as a by-product.

Numerous other objects and advantages will be apparent to those skilled in the art upon reading the accompanying specification, claims and drawings.

In the drawings The sole figure intthe drawings is a schematic diagram with the parts shown by conventional symbols of a carbon black producing plant embodying the present invention.

A carbon black furnace I is provided which preferably is constructed and operated' as set forth in the patents mentioned above, but which may be any carbon black furnace in which hydrocarbons are converted to carbon black by pyrochemical action and which furnace is adapted to produce increased quantities of tar containing carbon black by increasing thev hydrocarbon feed relative to the feed of free-oxygen containing gas, such as air.

Furnace I is provided with a reactant hydrocarbon feed 2 which is passed axially through the furnace and this hydrocarbon feed may be either oil from tank 3 or gas from line 4 orboth, valves 6 and I being opened or closed to vary the composition of feed 2, and feed 2 may be vaporized and/or preheated in vaporizer 8. At the same time free-oxygen containing gas, such as air 9, either with or vwithout fuel in the form of gas 4 and/or oil 3 coming through line II depending upon the position of valves 6 and I2, is blended by means of valves I3 and I4 and is injected tangentially into furnace I through pim I6. A portion of the hydrocarbon 2 and/or the fuel-II is burned in the free-oxygen Vcontaining gasA 9 in furnace I to heat the remaining portion of the hydrocarbon 2 to such an extent that,y pyrochemical f action converts a portion thereof to carbon black, and it is the intention in the present invention to so regulate the feeds to furnace I that a carbon black containing substantial quantities of tar is produced. If desired, some of air 9 may be admitted through valve I'I into a small annular space surrounding feed pipe 2 in order to reduce or obviate the formation of carbon black or tar on the end of` feed pipe 2 during long continued operation of furnace l. As all these features of furnace operation are fully disclosed in patents mentioned above they are only mentioned briey in this specification.

The tar content of the carbon black is determined by mixing 2 grams of black with 50 cc. of chloroform, boiling the mixture, filtering out the carbon black, and determining the percentage of light transmittance of the filtrate as compared with the transmittance of a blank sample of chloroform. Thecomparison ispreferably conducted with a photoelectric colorimeter. A carbon black containing tar which should be removed before it is commercially acceptable will have a filtrate which transmits less than 85% of the light transmitted by the blank sample of chloroform. As this is all ordinary laboratory procedure nothing vmentioned in this paragraph is shown in the drawings.

Itis customary to cool the resulting carbon black containing gases from furnace'l below the ignition or further reaction temperatures by any suitable means such as water jacket I8, water quench I9 and/or indirect heat exchange with the tion vessel 26 by any suitable means such as screw` conveyor 21. In the present drawing, screw conveyor 21 appears to be quite long, but this has no significance, as tank 26,c0uld be located directly under separatingl means 24, and conveyor 21 completely eliminated. However such conveyors can be used between elements if needed in the economic planning of the plant design.

The tar-containing black is preferably vigoronsly agitated by any suitable agitating means known to the prior artsuch as motor driven irnpeller 28, andv is mixed witha liquid solvent comprising essentially a chlorinated hydrocarbon.

Preferably the major portion, and in fact substantially all of said reactant solvent is a chlorinated hydrocarbon, having from 1 tov 3 carbon atoms andl n., chlorine atoms, in/ each molecule where n; is a numberfrom lrto a numberequal to 2 plus, twice the number of carbon atoms in each molecule, in orderto obtain the best results. Obviously minor additionsv of, other chemicals, such as hydrocarbons or oxygenated hydrocarbons, can be toleratedwithout undue reduction of the tardissolving power of the solvent, and their use should not be regarded as outside the scope of the present invention, but they should befregarded as in the nature of mereY diluents or added solventsfor usewith the solvent in the present process. While the chlorinated hydrocarbons having longer carbon chains in their molecules may in a number of instances be operable in the process,.

they, are not aseifective asthose with less than three carbon atoms, andA in fact the best results in the present process both as to extraction of tar in vessel 26 and as to the formation of hydrogen chloride in furnace I.is obtained byusinge chloroform, carbon tetrachloride, or ethylene d-ichloride.

The extraction of the tar is completed bypassing the carbon black, solvent and tar'slurry from vessel 26 tosettler 3| lthrough pipe32 where thee 4 solvent and contained tar is decanted through pipe 33 and wet carbon black is drawn off through pipe 34 controlled by valve 31 by gravity, or other conveying means (not shown) which may be like conveyor 21.

As the carbon black is the major product of the process its progress will be traced rst:

Wet carbon black 34 is introduced into a drying drum 36 by any suitable means. In order to ac- .celerate the drying it is generally preferable to have a burner 38 to heat the drying drum 3 6. The amount of solvent in a wet black 34 is relatively small and is driven off in the form of vapor in drum 36. As the amount is small it could be wasted to the atmosphere, but in large scale operations it is found that it is more economical to recover such, amounts of solvent by passing the same through pipe 39 to a solvent recovery system 4l which will be'discussed later. The dried carbon black coming from drum 36 is discharged into 'bin 42 generally inthe form of flocculent carbon black 43 as the drying drum 36 is generally operated under non-pelleting conditions. However, if desired, drum 36 can be operated to partially or completely pellet carbon black 43 at the same time the carbon black is being dried. It is regarded as preferable however to have a source of supply of flocculent carbon black 44 from bin 42 for those desiring such a product and then take-a portion 46 of said ilocculent carbon black and introduce it into a pelleting mill 41 by suitable means such as conveyor 48. Mill 41 is operated in the conventional manner to produce carbon black pellets 49 which are discharged into bin 5|.

The major portion 33'of the chlorinated hydrocarbon solvent containing dissolved tar is separatedrfrom said tar by any suitable separating means 56 and a majorY portion 51 of said-solvent then is recycledthrough line 29-by;any suitable means such as gravity orwpumps (not shown) to the extraction tank- 26, butthe following separating means and process are preferred:

The tar-containing solvent 33`is passed through a heater 52 under the pressure of pump 53A at such pressure anditemperature so that when this heated solvent is discharged through valve 54 into ash tank 56' the major portion of the solvent will turn into vapors and pass out line 5l for condensation in condenser 58 and return through line 29. Whatever quantity of makeup solvent is necessary is added through line 59. The tar along with EL minor proportion of solvent accumulates,` in the lower portion of ash tank 56 and is pumped into line 6I by pump 62; anywhere from 5) .to 95 per cent is vaporized in 5B.

At the same time, if solvent recovery 4l is ernployed, the vsolvent from wet carbon black 34 driven off in drying drum 36 and passing through line 3 9 isV preferably condensed in 4l by cooling and then instead of being added to line 23 this small amount -of tar-free solvent from 4i is pumped byy pumpV G3 into line Si, or it can be absorbed in 4l anddesorbed in cycles.

Thetar and solvent in line `6I is then added to the reactant hydrocarbon passing into furnace l andthis may be-done through one or more of lines-64, 66 and 61 depending' on the adjustment of theshutV off. valve-shown in each of these lines. The tar and solvent added through line 64 is preheated with the oil and/or gas from valve 6 and 1 in vaporizer, while that passing through line G6 is added to the hydrocarbon in itsgaseous state in line;2 andithatpassing through line 61 isaddeddirectly to ,the gas .inside furnace l. In

' the case of line 61 it can enter the furnace Athrough a pipe having an upper end adjacent the -end of line 2 so that the gases emerging from line 2 into the furnace tend to atomize and aspirate the tar and solvent from line 6l.

Due to the presence of chlorinated hydrocarbons in carbon black furnace I, off gas 23 will contain hydrogen chloride which kmay be sepa- `tor 8l. The remaining gas is withdrawn through line 'I I. The condensed aqueous HCl passes to a concentrator I3 where it is concentrated by evaporation to 15 to 36 Weight per cent HCl, which may be recovered as a by-product. Part of the concentrated aqueous HC1 is distilled with 90-98 per cent sulfuric acid in concentrator 'I6 te recover anhydrous HCl for recycle through line 'I3 or Withdrawal through Il. Aqueous H2SO4 is 'Withdrawn through line 83` for concentration and reuse.

Operation Hydrocarbon comprising gas 4, or oil 3, or mixtures thereof, is vaporized inv 3 and passed "through 2 into furnace I Where a portion is converted by pyrochemical action into carbon black.

I The resulting carbon black is cooled at I8, I9 and/or 2l and separated at 24 to produce carbon black 22 and olf gas 23.

' Carbon black 22 is extracted with a chlorinated 'hydrocarbon solvent in 26 as to its tar content and is separated in 3I and dried in 36 to form Aiiocculent black 44 or pelleted black 5I.

The solvent and contained tar from 3l is heated in 52 and the solvent flashed off in iiash tank 56.

The solvent passes overhead through 51 and condenser 58 back to the extraction tank 26.

The tar and some solvent from flash tank 56, along with solvent recovered at Ill from drying drum 36, is passed to the carbon black furnace I through line 6| and related lines Where a portion of it is converted to carbon black and hydroitangentially into furnace I through line I6 with or Without fuel added from valve I3 to provide oxygen for combustion in the furnace and this combustion is carried on to provide heat for pyrochemical action in converting a portion of the hydrocarbons, tar and chlorinated hydrocarbons to carbon black in furnace I.

'The hydrogen chloride in off gas 23 is removed vby a separating system which may comprise a "condenser 68 and Vessel 'I6 from which the hydrogen chloride is returned through a line 'I8 and associated lines to the carbon black furnace and some hydrogen chloride can be removed through line 'Il as a Icy-product of the process.

In the operation of the process best results are obtainable when the hydrocarbon feed 2 comprises essentially a refractory gas oil comprising aromatics and having an aniline point below 150 F. and an end bOiIing point less than 800 F.

xWhile air..9 is preferred for injection at I6 along "with natural gas as fuel from 4 which is injected Atangentially through I6 into furnace I, and the combustion substantially completed before contacting hydrocarbon 2, valuable results are also Y obtained by closing valve I3 and injecting straight air 9 through I6 to burn a portion of hydrocarbon 2 to produce the necessary heating effect. Chloroform is preferred as solvent 59.

While the system and its various component parts have been shown in considerable detail, this has been done for the purpose of illustrating a preferred embodiment of the invention, which invention is not limited thereto but is .definedby the following claims.

Having described my invention, I claim:

l. In a continuous furnace carbon black. producing process comprising the continuous steps `of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said hydrocarbon to carbon black by a pyrochemical cracking operation in a first zone in said furnace, cooling the effluent resulting carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said first Zone containing tar, extracting the tar from said carbon black with a liquid solvent comp-rising essentially a chlorinated hydrocarbon having from 1 to 3 carbon atoms and n chlorine atoms in each molecule, Where n is a number from 1 to a number equal to 2 plus twice the number of carbon 'atoms in each molecule, separating the major portion of said solvent from said extracted tar and recycling said major portion of said solvent to the extracting step, continuously adding the remaining solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said rst zone in said furnace in and by said same cracking operation that forms said carbon black, recovering said hydrogen chloride and said carbon black from said effluent gases cdntaining both hydrogen chloride and carbon black, continuously reicycling a portion of said hydrogen chloride to 'said furnace, drying said carbon black, recovering the chlorinated solvent from said drying step and continuously adding the recovered chlorinated solvent to said hydrocarbon passing int said furnace.

2. In a continuous furnace carbon black pro- 'ducing process comprising the continuous steps `continuously operating said furnace to produce a carbon black in said rst Zone containing tar,

' extracting the tar from said carbon black with a liquid solvent comprising essentially a chlorinated hydrocarbon, separating the major portion of said solvent from said extracted tar and recycling said major portion of said solvent to the extracting step, continuously adding the remaining solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said cracking operation that forms said carbon black,

recovering saidf..hydrogen.chloride; andsaidcar bon* black fromk said. eiiluent gases.; containing both hydrogen. chloride and; carbon. black; continuously recycling aA portion: ofV said. hydrogen chloride to said furnace, recoveringH the chlorinated solvent by. evaporation from said carbon black and continuously. adding the recovered chlorinated solvent to said hydrocarbon passing into said furnace.

3. In a. continuous furnace carbon black producingprocess comprising the continuousstepsof passing ahydrocarbon in a gaseous state into a carbon blackfurnace, heating said hydrocarbon in saidv furnace, converting a portion of said hydrocarbon to carbon black. by a pyrochemical crackingoperationiin` a first Zone insaid furnace, cooling the. efuent resultingcarbon black containing gases, and separating said carbon black from said. gases,. the improvementI comprising continuously operating said furnace to produce a carbon black in said firstzone containing tar, extracting'the tarfrom said carbon blackwith a liquid solvent comprising essentially a chlorinated hydrocarbon, continuously adding the solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said first zone in said furnace in and by said same cracking operation that forms said carbon black, recovering said hydrogen chloride and said carbon black from said effluent gases containing both hydrogen chlorider and carbon black, continuously recycling a portion of said hydrogen chloride to said furnace, drying said carbon black, recovering the chlorinated solvent from said drying step and continuously adding the recovered chlorinated solvent to said hydrocarbon passing into said furnace.

4. In a continuous furnace carbon black producing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said hydrocarbon to carbon black by' a pyrochemical cracking operation in a first Zone in said furnace, cooling the effluent resulting carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said first zone containing tar, extracting the tar from said carbon black with a liquid solvent comprising essentially a chlorinated hydrocarbon having from 1 to 3. carbon atoms and n chlorine atoms. in each molecule,

Where n is a numberfrom 1 to a number equal to 2 plus twice the number of carbon atoms in each molecule, continuously adding the solvent and tar mixture to the hydrocarbon passing' into said furnace, continuously forming hydrogen chloride by pyrochemical action in said'first zone.

in-said furnace in and by said same cracking operation that forms said carbon black, recovering said hydrogen chloride and said carbon black from said .eiuent gases containingboth hydrogen chloride and carbon black, continuouslyrecyclingA a. portion of said hydrogen chloride to said furnace and drying said carbon black..

5. In a continuous furnace carbonblack producing process comprising thecontinuous steps of passing a hydrocarbon in a gaseous state intol acarbon black furnace, heating said hydrocarbon in saidv furnace, converting a portion of said hydrocarbonto carbon black by a pyrochemical cracking operation in a first zone in said furnace,

'coolingtheefliuent resulting carbon blackoontaining gases;k and separating said carborrblaok from saicl'gases, `the -improvement comprisingl continuously operating said furnace to. produce. a carbon black.in.said first zone containing tar, extracting the tar from said carbon black with a liquid solvent comprising essentially a chlorinated hydrocarbon, continuously adding the-solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride. by pyrochemical action'in said first zone in saidv furnace in and by said same cracking operation that forms said carbon black, recovering said hydrogen chloride and said carbon black from said effluent gases containing both hydrogen chloride and carbon black, continuously recyclinga. portionof said hydrogen chloride to said furnace, drying said carbon black, recovering the chlorinated solvent. from said drying 4step and continuously adding the recovered chlorinated solvent to said hydrocarbon passingr into said furnace.

6. In acontinuous furnace carbon black pro-l ducing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion ofv said' hydrocarbon toi carbon black by a pyrochemical cracking operation in a first zone in said furnace, cooling the effluent resultingl carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said' furnace to produce a carbon black in paid first zonecontainingjtar, extracting the tar from said carbon black With a liquid solvent comprising essentially a chlorinated hydrocarbon, separating theY major portion of said solvent from said extracted tar andrecycling saidmajorportion of said solvent tothe extracting step, continuously addingthe remaining solvent and tar mixture to the hydrocarbon passing into said furnace,A continuously forming hydrogen chloride by pyrochemical action in said first zone in said furnacein and by said same cracking operationthat forms said carbon black, recovering saidA hydrogen chloride and said carbon black from said effuent gases containing both hydrogen chloride and carbon black, continuously drying saidcarbonblack.

7. In a continuous furnace carbon black producing process comprising the continuous steps of passing. a hydrocarbon in a gaseous state .into a carbon black furnace, heating said hydrocarbon in said furnace, `convertinga portion of said hydrocarbon to carbon black by a Vpyrochemical crackingoperation in a first zone in said furnace, cooling the effluent resultingcarbon-black containinggases, and separating said carbonvk black from. said gases, the improvement comprising continuouslyY operating .said furnace toV produce'a carbon blackin saidfirst zone containing tar, extracting the tarl from said carbon'blacktwith a liquid solvent comprising essentially. aV chlorinated hydrocarbon having from'l to 3 carbon atoms and n chlorine atoms in each molecule, Wheren is a number from 1.to anumber equal to 2 plus twice the number of carbon atoms in each molecule,` separating the major. portionof said solvent from said extracted tarand recycling said major portionV of said solvent to the extracting step, continuously addingthe'remaining.. solvent and'tar mixture to the hydrocarbon passing into said furnace, continuously forming. hydrogen chloridebypyrochemical action in said` first zone -in saidfurnacev in and. by said samencrackingfoperation that forms said carbon .black,.recovering said hydrogen chloride and said carbon black from said eilluent gases containing both hydrogen chloride and carbonblack, continuously drying` said carbon black.

8. .In a continuous furnace carbon black producing process comprising the continuous steps o f passing a hydrocarbon in a gaseous stateinto a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion Iof said hydrocarbon to carbon black by a pyrochemical cracking operation in a rst Zone in said furnace, cooling the effluent resulting carbon black containing gases, and separating said car-bon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said rst zone containing tar, extracting the tar from said carbon black With a liquid solvent comprising essentially a chlorinated hydrocarbon having from 1 to 3 carbon atoms and n chlorine atoms in each molecule, where n is anumber from 1 to a number equal to 2 plus twice the number of carbon atoms in each molecule continuously adding the solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said rst Zone in said furnace in and by said same cracking operation that forms said carbon black, recovering said hydrogen chloride and said carbon black from said effluent gases containing both hydrogen chloride and carbon black, continuously, and recycling a portion of said hydrogen chloride to said furnace.

9. In a continuous furnace carbon black producing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace', converting a portion of said hydrocarbon to carbon black by a pyrochemical cracking operationl in a rst zone in said furnace, cooling the efliuent resulting carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said rst Zone containing tar, extracting the tar from said carbon blackvvith a liquid solvent comprising essentially a chlorinated hydrocarbon, continuously adding the solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said first zone in said furnace in and by said same cracking operation that forms said carbon black, recovering said hydrogen chloride and said carbon black from said effluent gases containing both hydrogen chloride and carbon black, continuously, and recycling a portion of said hydrogen chloride to said furnace.

10. In a continuous furnace carbon black producing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said hydrocarbon to carbon black by a pyrochemical cracking operation in a first Zone in said furnace, cooling the effluent resultingA carbon black containinggases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said first zone containing tar, extracting the tar from said carbon black With a liquid solvent comprising essentially a chlorinated hydrocarbon having from 1 to 3 carbon atoms and n chlorine atoms in each molecule, where n is a number from 1 to a number equal to 2 plus twice the number of carbon atoms in 10' each molecule separating the major portion of Said solvent from said extracted tar and recycling said major portion of said solvent to the extracting step, continuously adding the remaining solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said rst zone in said furnace in and by said same cracking operation that forms said carbon black and recovering said hydrogen chloride and said carbon black from said effluent gases containing both hydrogen chloride and carbon black, con-l tinuously.

11. In a continuous furnace carbon black pro-V ducing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said hydrocarbon to carbon black by a pyrochemical cracking operation in a first zone in said furnace, cooling the eilluent resulting carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said first zone containing tar, extracting the tar from said carbon black with a liquid solvent comprising essentially a chlorinated hydrocarbon, separating the major portion of said solvent from said extracted tar and recycling said major portion of said solvent to the extracting step, continuously adding the remaining solvent and tar` mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said first zone in said furnace in and by said same cracking operation that forms said carbon black and recovering said hydrogen chloride and said carbon black from said effluent gases containing both hydrogen chloride and carbon black, continuously.

12. In a continuous furnace carbon black producing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said =hydrocarbonto carbon black by a pyrochemical cracking operation in a rst zone in said furnace, cooling the eflluent resulting carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said rst zone containing tar, extracting the tar from said carbon black with a liquid solvent comprising essentially a chlorinated hydrocarbon, continuously adding the solvent and tar mixture to the hydrocarbon passing into said furnace, continuously forming hydrogen chloride by pyrochemical action in said first zone in said furnace inand by said same cracking operation that forms said carbon black and recovering said hydrogen chloride and said carbon black from said eiiiuent gases containing both hydrogen chloride and carbon black, continuously.

13. In a'continuous furnace carbon black producing process comprising the continuous steps of passing a hydrocarbon in a gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said hydrocarbon to carbon black by a pyrochemical cracking operation in a first zone in said furnace, cooling the effluent resulting carbon black containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to'produce a carbon black in said rst zone containing tar,

extracting the 4tar from --said carboni-black with a liquid -solvent -comprising essentially Va chlorinated hydrocarbon Ahaving from 1 to 3 carbon atoms and 'n chlorine atoms in each molecule, where n is a number from -1 to a -number equa] to-Z plus twice the numberof carbonatoms 'in each molecule, separating the major lportion of said `solvent from said extracted tar and recycling said -major portion of said solvent to the extracting step, continuously adding the remaining sclventfand tarmixture to the hydrocarbon passing into said furnaceand continuously forming hydrogen chloride by pyrochernical action in said first zone in said furnace in and by said same cracking operation that forms said carbon black.

14. In a continuous -furnace carbon black producing process comprising the continuous steps of passinga-hydrccarbon in a gaseous state into a carbon 'black-furnace, heating said hydrocarbon inv-said furnace, converting a portion of said hydrocarbon to carbon black by a pyrochemical cracking operation inra firstzone in saidfurnace, cooling the eluent resulting carbon black containing gas es, and rseparating said carbon-black from said gases, the improvement comprising continuouslyoperating said furnace to Vproduce a-carbon black-in said rst Zone containing tar, extracting the'tar fromsaid carbon black with aliqud solvent comprising essentially a chlorinatedhydrocarbon, separating vthe major portion of said solvent from said extracted tar and recycling said7majo1portion of said solvent to the extracting step, continuously adding theremainingsolvent and tar mixture to the hydrocarbon passing'in'to said-furnace and continuously forming lhydrogen ychloride by1pyrochemica1 action i2 in said Afirst yzone v in I' said furnace in f and lby said same -cracking operation thatforms said-carbon black.

15. In a continuous furnace carbo'nblack producing process comprising the continuous Vsteps of Vpassing a hydrocarbon ina-gaseous state into a carbon black furnace, heating said hydrocarbon in said furnace, converting a portion of said hydrocarbon ,to carbon black by a pyrochemical cracking operation in a rstzone in-saidfurnace, cooling the eiiiuent'sresulting-carbon black 'containing gases, and separating said carbon black from said gases, the improvement comprising continuously operating said furnace to produce a carbon black in said 'rst zone containing tar, extractingthe tar from said carbon black with a liquid solvent comprisingessentially a chlorinated hydrocarbon, continuously addingthe solvent and tar mixture to the hydrocarbon passing into said .furnace and continuously forming hydrogen chloride'by pyrochemical Aaction in said rst zone in 'said-furnace in and byfsaid same cracking operation that 'forms said carbonblack.

"GEORGE ,'N. CADE.

REFERENCES CITED The Afollowing references are of record in the file of this patent:

UNITED STATES `.PATENTS Number Name Date 1,259,121 Mott Mar. 12, 1918 1,990,228 Frenkel Feb. ,5, 1935 2,238,576 Heller et al Apr. 15, 1941 2,375,795 Krejci May 15, .1945 

1. IN A CONTINUOUS FURNACE CARBON BLACK PRODUCING PROCESS COMPRISING THE CONTINUOUS STEPS OF PASSING A HYDROCARBON IN A GASEOUS STATE INTO A CARBON BLACK FURNACE, HEATING SAID HYDROCARBON IN SAID FURNACE, CONVERTING A PORTION OF SAID HYDROCARBON TO CARBON BLACK BY A PYROCHEMICAL CRACKING OPERATION IN A FIRST ZONE IN SAID FURNACE, COOLING THE EFFLUENT RESULTING CARBON BLACK CONTAINING GASES, AND SEPARATING SAID CARBON BLACK FROM SAID GASES, THE IMPROVEMENT COMPRISING CONTINUOUSLY OPERATING SAID FURNACE TO PRODUCE A CARBON BLACK IN SAID FIRST ZONE CONTAINING TAR, EXTRACTING THE TAR FROM SAID CARBON BLACK WITH A LIQUID SOLVENT COMPRISING ESSENTIALLY A CHLORINATED HYDROCARBON HAVING FROM 1 TO 3 CARBON ATOMS AND N CHLORINE ATOMS IN EACH MOLECULE, WHERE N IS A NUMBER FROM 1 TO A NUMBER EQUAL TO 2 PLUS TWICE THE NUMBER OF CARBON ATOMS IN EACH MOLECULE, SEPARATING THE MAJOR PORTION OF SAID SOLVENT FROM SAID EXTRACTED TAR AND RECYCLING SAID MAJOR PORTION OF SAID SOLVENT TO THE EXTRACTING STEP, CONTINUOUSLY ADDING THE REMAINING SOL- 